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<h1><a href="https://archiveofourown.org/works/23047897">How the bending genetics of Avatar: The Last Airbender work: An analysis</a> by <a class='authorlink' href='https://archiveofourown.org/users/AtarahDerekh/pseuds/AtarahDerekh'>AtarahDerekh</a></h1>

<table class="full">

<tr><td><b>Category:</b></td><td>Avatar: Legend of Korra, Avatar: The Last Airbender</td></tr>

<tr><td><b>Genre:</b></td><td>Bending (Avatar), Genetics, Sort Of, scientific analysis</td></tr>

<tr><td><b>Language:</b></td><td>English</td></tr>

<tr><td><b>Status:</b></td><td>Completed</td></tr>

<tr><td><b>Published:</b></td><td>2020-03-07</td></tr>

<tr><td><b>Updated:</b></td><td>2020-03-07</td></tr>

<tr><td><b>Packaged:</b></td><td>2021-05-01 05:42:20</td></tr>

<tr><td><b>Rating:</b></td><td>General Audiences</td></tr>

<tr><td><b>Warnings:</b></td><td>No Archive Warnings Apply</td></tr>

<tr><td><b>Chapters:</b></td><td>1</td></tr>

<tr><td><b>Words:</b></td><td>3,284</td></tr>

<tr><td><b>Publisher:</b></td><td>archiveofourown.org</td></tr>

<tr><td><b>Story URL:</b></td><td>https://archiveofourown.org/works/23047897</td></tr>

<tr><td><b>Author URL:</b></td><td>https://archiveofourown.org/users/AtarahDerekh/pseuds/AtarahDerekh</td></tr>

<tr><td><b>Summary:</b></td><td><div class="userstuff">
              <p>A study of how bending is expressed in ATLA, with special emphasis on the Air Nomads, Katara and the Southern Water Tribe, and Piandao.</p>
            </div></td></tr>

<tr><td><b>Comments:</b></td><td>4</td></tr>

<tr><td><b>Kudos:</b></td><td>30</td></tr>

</table>

<a name="section0001"><h2>How the bending genetics of Avatar: The Last Airbender work: An analysis</h2></a>
<div class="story"><div class="fff_chapter_notes fff_head_notes"><b>Author's Note:</b><blockquote class="userstuff">
      <p>In a format vaguely reminiscent of APA style. No citations included.</p>
    </blockquote></div><div class="userstuff module">
    
    <p>Introduction:<br/>
The hard magic system in the world of Avatar: The Last Airbender (ATLA) takes the form of the manipulation of the four classical elements; those being fire, air, water and earth. This manipulation is known as bending. Bending is well developed, being based on several Chinese martial arts forms—most notably kung fu and tai chi—but is vaguely explained beyond its mechanics. It is established early on that not every person in the world is a bender. The actual percentage of benders is unknown, but there appears to be a general consensus that an estimated 30% of the world's inhabitants are benders. The element an individual is able to bend is genetic, the sole exception being the avatar, of which only one can exist at a time. Even in that regard, the avatar's “native element” is determined by his or her genetic heritage. Even for an avatar of mixed race, such as Kyoshi, the native element must be associated with one of the avatar's parents. However, whether or not a person is a bender at all seems to be much less dependent upon genetics, at least as far as they are understood in terms of inherited traits. That is to say that the ability to bend is neither a recessive nor a dominant trait, and it can be argued that the genetic capacity for bending is thus present in the entire human population of the ATLA world. However, bending only manifests in a given percentage of individuals within a given nation, with some nations having higher percentages of benders than others overall. This is allegedly linked to a given nation's spirituality, with the Air Nomads historically having a population comprised entirely of airbenders, and the Earth Kingdom having the lowest percentage of benders. The Air Nomads are upheld as the most spiritual of the nations, while the Earth Kingdom is regarded as the least spiritual. Additionally, whether an individual is a bender or not seems to have little to nothing to do with the number, strength or spirituality of benders in his or her family line. In particular, this analysis will take a look at the decline of waterbending in the Southern Water Tribe, with special focus on Katara, the first waterbender born in over half a century in her tribe. We will also be hypothesizing how Master Piandao of the Fire Nation, born to two powerful firebenders, is himself a non-bender. These two nations will be compared to the Air Nomads, whose bending population was originally 100%. The goal is to answer the question of if and how spirituality and external stresses play a role in bending populations and the manifestation of bending abilities in the individual.</p><p>Methods:<br/>
To establish how bending is passed from generation to generation, we will first establish the genetic capacity for bending. ATLA and its sequel series, Legend of Korra (LOK), showcase several characters that help to establish the fact that the ability to bend is not strictly inherited. Katara of the Southern Water Tribe is born to two non-benders, while Piandao of the Fire Nation and Bumi II, son of Avatar Aang and Katara, are both non-benders (initially, in the latter's case) born to parents who were both prodigy benders. There are also multiple sets of twins shown in both series. One seemingly identical set is comprised of a non-bender and an earthbender, while a set of fraternal twins is comprised of two waterbenders. If bending were simply a matter of a recessive or dominant trait, clear patterns would emerge among parents and offspring. If, for example, bending were a dominant trait, there would be a 25% chance that two bending parents would have a non-bending child (assuming both parents carry the recessive gene), but no chance at all that two non-bending parents would have a bending child. If bending were a recessive trait, the inverse would result. In either case, it would be impossible for identical twins to have mixed bending abilities, or for Katara to be a bender in a world where Piandao and Bumi are not. In the opening episode of ATLA, Katara establishes that waterbending is a sacred art unique to her culture, suggesting that bending is potentially inherent to every person within that culture, even if it never manifests. Thus we will work with the hypothesis that the genetic capacity for bending is present in 100% of the population, but only manifests when certain conditions are met.</p><p>To understand the conditions that are favorable for producing benders, we will take a look at the impact that the 100 Year War had on the Air Nomads and the Southern Water Tribe. The Air Nomads, as is well recorded, were rendered functionally extinct due to the genocide imposed on them by Fire Lord Sozin. However, it is well known that not every single airbender was killed in the initial attack, and that only one inhabitant of the Southern Air Temple died in said assault. The survivors went into hiding, leading Sozin to believe (correctly) that his target, Avatar Aang, was still alive. By the time Aang reemerged, airbending had gone extinct in the world, its last remaining practitioners either having been systematically hunted down and killed over the course of a century, or having died of old age deep in hiding within the remaining nations. This leaves open the possibility of descendants of mixed Air Nomad race, none of whom manifested any airbending ability until harmonic convergence, 170 years after the genocide (AG). There is also documentation of mixing between the Air Nomads and other nations prior to the genocide, but the rate at which these mixes produce airbending offspring—or bending offspring at all—is unknown, as the best documented case is Avatar Kyoshi, whose native element was earth, but who was, of course, also an airbender. Regardless of what we know about the rate at which airbenders of mixed ancestry are born under normal circumstances, we can be certain of two things: 1) there were survivors of the genocide who lived long enough to potentially leave descendants, and 2) if they did, none of those descendants were airbenders as of 100 AG.</p><p>Turning to the Southern Water Tribe, we see another attempted genocide, this one targeting waterbenders specifically, with non-benders generally being spared. Under the rule of Fire Lord Azulon, the Fire Nation sanctioned raids by privateers on the Southern Water Tribe to capture their waterbenders based on the possibility that one of them could be the new avatar. These raids began sometime around 40 AG and continued for about 10 years in total. It was at about this time that the Fire Nation determined there were no waterbenders remaining in the Southern Water Tribe. Nonetheless, Azulon had the Southern Water Tribe monitored closely in case another waterbender should appear. Around half a century passed between the capture of the last southern waterbender and the birth of the next southern waterbender. During this time, the tribe's focus turned to survival and rebuilding, and spirituality appeared to decline among the splintered and scattered tribes. But there is no indication that the tribe's spiritual nature ever disappeared entirely, as tribal elders such as Kanna kept spirituality alive by teaching the history of waterbending to new generations. The odds should therefore favor a waterbender being born closer in age to the elders who survived the raids, yet there is a notable gap in time between the previous waterbenders and the new generation of waterbenders—as much as three possible generations. When Katara manifested waterbending abilities, it drew the Fire Nation back to her village, and after that raid that resulted in the death of Katara's mother, no waterbenders were born in that village in the following six years. However, in a nearby, untouched village, not one but two waterbenders were born to the same parents in that timespan, to be discovered after the war had concluded, when it was safe for them to reveal their abilities. During the final few years of the war, both children had been instructed to hide their bending at all costs, suggesting that bending was feared for the repercussions it might bring. This also suggests that the spiritual aspect of bending was not something that was highly valued in that particular village, which brings into question how the spirituality of the parents or community supposedly influences the manifestation of bending.</p><p>Finally, we must consider the Fire Nation itself. Fire Lord Sozin began the war on the day of the arrival of a near-earth comet that would later be renamed for him. This comet enhanced firebending 100 times over. In utilizing the comet, Sozin stacked his military with firebenders, and thus firebending became a preferred trait for service members over the course of the war. We observe throughout ATLA that the overwhelming majority of Fire Nation military personnel are firebenders, including possibly every member of the crew of the Wani, Prince Zuko's ship. Yet among civilians within the Fire Nation proper, most appear to be non-benders. The percentage of benders within the colonies is unknown. But it can be concluded that firebenders are more often drafted into service, end up serving longer, and have more opportunities for advancement. Because firebenders comprise the majority of the military, they also comprise the majority of war casualties. Thus firebenders on average have lower survival rates and a lower average lifespan, often leaving behind parents. Regions of the Fire Nation renowned for producing powerful, skilled firebenders would be expected to contribute more manpower to the war effort than regions that generally do not have a notable firebending population. Thus the pressure would be on these regions to produce more firebenders, yet there would also be pressures on their populations overall when their firebending children fail to return from war. These factors both seem to be unrelated to a given region's overall spirituality, with no known rates of firebending occurrence in regions that are governed by fire sages. It can be assumed that since bending is perceived as being directly influenced by spirituality that spirituality would thus be considered a high priority in regions pressured to produce the best firebenders. This, in combination with selective breeding for strong firebenders, would have been the conditions under which Piandao was born. Yet he was not a firebender, despite the best efforts of his family and community to assure that he would be one. The fact that he was abandoned upon discovery that he was a non-bender suggests a highly hypocritical component to the Fire Nation's sense of spirituality, but we observe throughout LOK that the spirits of that world generally do not concern themselves with hypocrisy, even engaging in it themselves routinely. Thus we can conclude that the purpose behind one's spirituality is apparently not as important as simply being spiritual. Piandao himself grew up to be a highly spiritual man despite the hypocrisy he fell victim to as a young child. This apparent disconnect between genuine spirituality and firebending further serves to indicate that the manifestation of bending is not strictly linked to spirituality, if it is at all.</p><p>In our own world, recent genetic research has revealed that the expression of genetic information is not simply a matter of which genes are dominant and which are recessive. Some genes, it has been found, can be repressed in favor of another gene being expressed instead. A given gene can be “switched off” by proteins known as epigenetic markers, preventing it from being expressed. Furthermore, these genetic switches can be and are routinely “flipped” within a generation, or even within an individual specimen. The action of epigenetic markers appears to be triggered largely by environmental factors, with population stresses affecting gene expression between generations, and immediate survival stresses affecting expression within individuals. In a developing fetus, a gene's expression may be repressed in response to a temperature or chemical indicator from the surrounding environment—in the case of placental mammaloids, by the hormonal responses of the mother to types of stress (examples in egg laying species include temperature-dependent sex determination). It is these epigenetic markers that could be the key to understanding the manifestation of bending in a given population in the ATLA world, assuming genetic expression works in a similar manner among carbon-based life forms—humans in particular—in that world.</p><p>Results:<br/>
Applying the concept of epigenetic markers to the manifestation of bending offers a reasonable explanation for why bending is expressed or not expressed in a given population, and in particular why it might be suddenly repressed in a population that historically had a high occurrence of benders. It should be noted that epigenetic markers and the conditions that trigger them are not fully understood, but that it is well documented that some genes in identical twins can indeed be switched off in one twin, but left on in another. This would explain why, in our previous example, one twin in a set of identicals might be an earthbender, while the other is not. But in the case of a sudden decline in the occurrence of bending among a given population, the cause seems to be more readily apparent.</p><p>In the case of the Air Nomads, the introduction of new genetic information was likely part of the reason for the decline of airbending. As demonstrated by Aang and Katara, the combination of Air Nomad genetics with those of the Water Tribe can result in offspring who are waterbenders, airbenders or non-benders. The spirituality of the community and parents seems to have no influence here whatsoever, as Aang, being both an Air Nomad and the avatar, is arguably the most spiritual person of his time, choosing to reside in places that he considers to be inherently spiritual. And yet he had as his firstborn a non-bender. A working hypothesis for the reemergence of airbending is that all its recipients—among whom was Bumi II—are descended from Air Nomads, and whose ancestors never manifested airbending in the 170 years between the start of the war and harmonic convergence. The repression of airbending can be easily explained not just by the “diluting” of Air Nomad blood due to interracial marriage, but also by epigenetic markers responding to the extreme stress placed upon the Air Nomads by genocide. Since the expression of airbending came with a virtual 100% chance of being killed before reaching maturity, the gene was switched off.</p><p>

A near-identical case happened in the Southern Water Tribe. When a pattern emerged demonstrating that waterbenders had a 100% chance of being removed from the gene pool, the epigenetic marker for the expression of waterbending probably shut the gene down completely until such a time as that particular environmental stress was no longer apparent. This took two generations in the case of Katara's village, which is a reasonable amount of time for an environmental stress on a population to ease up. It likely took longer for other villages, even with the addition of bloodlines from the Northern Water Tribe. Even within Katara herself, the tendency for the bending gene to be repressed was still strong, as made evident by her firstborn being a non-bender initially, though it was later discovered that he did indeed have the genetic capacity for airbending.</p><p>Similar circumstances may have arisen in certain regions of the Fire Nation, where pressure was high to produce strong firebenders fit for military service, and which therefore suffered greater losses to their overall population as casualties of war. These pressures may have been felt by the people of Piandao's hometown, resulting in the repression of the bending gene, reducing the birth rate of firebenders, and preserving the remaining population. This would have happened independent of any spiritual influence, and Piandao likely would not have been the only non-bender born to firebending parents in his era. As non-benders were more likely to survive the war, return home and reproduce, non-bending was a biologically favorable trait of that time and place, even if it was not a socially favorable one.</p><p>Discussion:<br/>
From everything that we can observe about the workings of bending in the world of ATLA, there does not appear to be a strong correlation between bending and spirituality. While it's true that the Air Nomads were historically regarded as the most spiritual of nations with the highest percentage of benders, and the Earth Kingdom came into last place in both aspects, this does not offer particularly strong evidence of correlation. The Air Nomads were also pacifists who avoided conflict, while the Earth Kingdom has historically been rife with conflict. Thus the Air Nomads previously had little to no environmental stresses on them that might reduce their bending populations, while the Earth Kingdom consistently has. Much more likely is the probability that the manifestation of bending abilities is due to epigenetic markers dictating the expression of bending genes.</p><p>This also offers an explanation for the working of energy bending—that is, the ability to bestow or remove bending abilities within an individual. In ancient times, the lion turtles practiced energy bending, allowing bending to be expressed or repressed in turn in individuals as they required it. When the lion turtles renounced their role as the “keepers” of bending, they bestowed the ability on a certain percentage of the population, and from there it became ingrained in the genetics of the human race. The lion turtles imply that, with the exception of the avatar, the expression of one type of bending comes at the cost of the expression of other types of bending; something we can see demonstrated in LOK by the half-Water, half-Air siblings Kya and Tenzin (and later Bumi), and by the half-Fire, half-Earth brothers Mako and Bolin. Energy bending likely involves the direct manipulation of epigenetic markers, allowing bending to be forcibly switched on or off within the individual. This explains how Aang was able to remove the bending of such criminals as Ozai and Yakone, and Korra was able to restore the bending of Lin Beifong, who had suffered bloodbending applied directly to her brain at the hands of Yakone's son Noatak (the terrorist known as Amon), which had effectively blocked her earthbending altogether. It would also explain why energy bending is an avatar-level skill, as it requires a finesse that far exceeds even that of bloodbending to block chi without killing the victim. Of course, this hypothesis does raise the question of whether it's possible for the avatar to bestow bending on an individual who never manifested it to begin with, or if the avatar might be able to “switch” the elements of a bender of mixed heritage (e.g. make Tenzin a waterbender instead of an airbender). As we have no precedent whatsoever for such scenarios, they will remain in the realm of imagination.</p><p>Summary:<br/>
The expression of bending appears to not be directly connected to one's spirituality as was previously believed. It appears instead to be genetically inherent to 100% of the ATLA world population, but whether or not it is expressed depends on epigenetic markers that turn the genes for bending on or off based on a variety of environmental factors and stresses. These markers can be directly manipulated by energy bending, and more exploration on the subject of energy bending as it pertains to epigenetic markers is necessary for greater understanding. As it stands now, the decline of bending among the Air Nomads and Southern Water Tribe, as well as the low occurrence of bending within the perpetually turbulent Earth Kingdom, is most likely due to the repression of the bending genes as a response to extreme environmental stresses on each of those populations. This is also the most likely explanation for the repression of the firebending gene in Piandao.</p>
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